Plasma and intestinal concentrations of GIP and GLP-1 (7-36) amide during suckling and after weaning in pigs

Plasma concentrations of glucose dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1(7-36)amide (GLP-1[7-36]amide) were measured after milk ingestion in 15-18 day old piglets and after weaning diet ingestion in 33 day old piglets weaned at 21 days. Intestinal concentrations of these two hormones were also measured in unsuckled piglets of less than 24 h of age, and piglets whose ages corresponded with those used for plasma measurements. Suckling piglets showed a moderate glycaemic and insulinaemic response to milk ingestion. Plasma GIP and GLP-1(7-36)amide levels were significantly elevated at 1 and 3-h post-prandially. Weaned piglets showed a much more marked glucose and insulin response to meal ingestion. Plasma GIP and GLP-1(7-36)amide levels were again significantly elevated at 1 and 3 h in these animals. The mean plasma GIP response was greater in the weaned animals compared with the suckling animals at the time points investigated. The plasma GLP-1(7-36)amide response in contrast was significantly greater at 1 h in the suckling animals. In comparison, GIP concentrations in acid ethanol extracts of the small intestine were significantly higher during suckling and GLP-1(7-36)amide concentrations significantly higher after weaning. The circulating levels of both hormones seen during suckling and after weaning were far higher than those previously reported in humans. We conclude that both milk ingestion and the weaning diet are capable of stimulating GIP and GLP-1(7-36)amide in piglets and suggest that the levels of both hormones seen in this study may be important in adipose tissue metabolism at this time.

Octreotide exacerbated fasting hypoglycaemia in a patient with a proinsulinoma; the glucostatic importance of pancreatic glucagon

Octreotide, a long-acting somatostatin analogue, has been used to alleviate hypoglycaemia in patients with insulinomas. Transient worsening of fasting hypoglycaemia following octreotide has also been described (Stehouwer et al., 1989). We describe a patient with a 'proinsulinoma' in whom octreotide caused rapid and prolonged symptomatic worsening of fasting hypoglycaemia. Catecholamine and cortisol counterregulatory hormonal responses were normal but those of glucagon and GH were impaired. Acute neuroglycopaenic symptoms were present during octreotide induced hypoglycaemia, which was accompanied by and attributed to an acute reduction in pancreatic glucagon secretion in the presence of persistent and unsuppressed hyperproinsulinaemia. This suggests that glucagon may be important in maintaining glucose homeostasis in chronic hypoglycaemia due to endogenous hyperinsulinism even though its concentration in the peripheral blood is not raised.

GIP and GLP-1(7-36)amide secretion in response to intraduodenal infusions of nutrients in pigs

Investigation of nutrient stimulation of two gut hormones GIP (glucose dependent insulotropic polypeptide) and GLP-1(7-36)amide (the active truncated form of glucagon-like peptide-1) is made difficult by the differential control of gastric emptying. Direct nutrient infusion into the duodenum was therefore carried out on three female pigs. The infusates consisted of saline (0.85 g or 1.7 g/100 ml); glucose (20 g or 40 g/100 ml); fat (30 g or 60 g/500 ml) and glucose/fat (20 g and 30 g or 40 g and 60 g per 1000 ml). Plasma glucose levels were elevated as expected by glucose or glucose/fat infusions, and they were not affected by the presence of fat in the infusate. Insulin secretion was stimulated in the presence of glucose or glucose/fat. Plasma triacylglycerol was elevated following fat and glucose/fat infusions. The greatest stimulus for GIP secretion was glucose/fat (P < 0.05); fat alone was a poor stimulus for GIP secretion, but glucose was a potent stimulus. GLP-1(7-36)amide was moderately stimulated by glucose and markedly stimulated by fat and glucose/fat infusions (P < 0.05). We conclude that, in pigs, dual nutrient infusion of glucose/fat is a strong stimulus for both GIP and GLP-1(7-36)amide secretion. The hormones therefore have the potential to play an important physiological role, both in the stimulation of insulin secretion and in adipose tissue metabolism in pigs.

Mechanisms of airway protection after pharyngeal fluid infusion in healthy sleeping piglets

The airway protective mechanisms evoked after infusion of fluids into the pharynx were examined in the intact and healthy newborn piglet during sleep. Thirteen healthy normothermic piglets (3-6 days of age) were examined on 4 consecutive days during sleep. The fluids infused (0.05-1.5 ml) were 0.9% saline, distilled water, and HCl (pH 3 and pH 2). Respiratory rate, heart rate, oxygen saturation (SaO2), swallowing, and arousal were compared pre- and postinfusion during active (AS) and quiet sleep (QS) for each test fluid. The most common response in AS and QS was swallowing (90%) and then arousal (24%); however, no apnea occurred, and respiratory rate and SaO2 were always maintained. A significant difference occurred between HCl infusions of pH 2 and pH 3; at pH 2, the frequency of swallows and latency to the first swallow were reduced (P < 0.05) and the frequency of arousal was reduced in AS compared with that in QS (P < 0.01). Airway protection after pharyngeal fluid stimulation is achieved primarily by swallowing and arousal, without any effect on respiratory rate and SaO2. Attenuation of protective mechanisms occurred, however, when the infusate was at pH 2.

Hypopituitarism in primary haemochromatosis; recovery after iron depletion

We report a case of primary haemochromatosis complicated by anterior hypopituitarism which recovered after aggressive venesection therapy. Reversal of anterior hypopituitarism in haemochromatosis following iron depletion has not been previously described.

Hyperinsulinaemia of hypertriglyceridaemia: a reappraisal

The peripheral hyperinsulinaemia of hypertriglyceridaemic subjects has only been defined using insulin immunoassays in which proinsulin and proinsulin fragments cross-react. Relative contributions of pancreatic secretion and hepatic extraction of insulin to this hyperinsulinaemia have not been studied. We, therefore, reassessed the hyperinsulinaemia of hypertriglyceridaemia by measuring fasting plasma concentrations of intact proinsulin, glucose, insulin, and C-peptide in 24 hypertriglyceridaemic subjects with normal glucose tolerance (n = 14) and with impaired glucose intolerance (n = 10) and in normal subjects (n = 14). Hypertriglyceridaemic subjects had higher (p < 0.01) fasting concentrations of insulin and C-peptide and greater (p < 0.01) fasting insulin: C-peptide molar ratios than in control subjects. Fasting intact proinsulin concentrations were similar in hypertriglyceridaemic subjects with normal glucose tolerance and control subjects but these were lower (p < 0.01) than in hypertriglyceridaemic subjects with impaired glucose tolerance. These results suggest that the fasting peripheral hyperinsulinaemia of hypertriglyceridaemic subjects is due to increased pancreatic secretion and reduced hepatic fractional extraction of insulin. The peripheral hyperinsulinaemia of hypertriglyceridaemia appears to reflect peripheral insulin resistance and is not attributable to elevated proinsulin concentrations which are characteristic of impaired glucose tolerance and Type 2 (non-insulin-dependent) diabetes mellitus.

Insulin in ischaemic heart disease: are associations explained by triglyceride concentrations? The Caerphilly prospective study

OBJECTIVE

To investigate the predictive value of fasting insulin concentrations for subsequent fatal or non-fatal ischaemic heart disease at five year follow up and to examine the associations between insulin and other indicators of risk.

DESIGN

A prospective population study among 2512 men aged 45 to 59 at recruitment.

SETTING

A whole population sample of men resident in Caerphilly, South Wales.

MEASUREMENTS

At recruitment fasting blood samples were taken for measurement of plasma lipids and serum insulin. Men were re-examined at a five year follow up and ischaemic heart disease events during this period were assessed from hospital notes, death certificates, and electrocardiograms.

MAIN RESULTS

Diabetic men and those men with a fasting blood glucose of > or = 8 mmol/l were excluded from all analyses. In a univariate analysis the incidence of ischaemic heart disease increased with increasing concentration of fasting insulin, such that for men in the top 20% of the insulin distribution the odds of developing ischaemic heart disease were 1.87 relative to men in the bottom 20%. On multivariate analysis this relation disappeared on adjusting for plasma triglycerides, body mass index, and evidence of ischaemic heart disease at recruitment.

CONCLUSION

In this population in South Wales there was no evidence that the fasting insulin concentration is an independent risk factor for ischaemic heart disease. The univariate association between insulin and incident disease was almost entirely explained by the association of both with triglycerides and body mass index.

Glucagon-like peptide-1 (7-36)amide and glucose-dependent insulinotropic polypeptide secretion in response to nutrient ingestion in man: acute post-prandial and 24-h secretion patterns

The acute effects of different macronutrients on the secretion of glucagon-like peptide-1(7-36)amide (GLP-1(7-36)amide) and glucose-dependent insulinotropic polypeptide (GIP) were compared in healthy human subjects. Circulating levels of the two hormones were measured over a 24-h period during which subjects consumed a mixed diet. In the first study, eight subjects consumed three equicaloric (375 kcal) test meals of carbohydrate, fat and protein. Small increases in plasma GLP-1(7-36) amide were found after all meals. Levels reached a maximum 30 min after the carbohydrate and 150 min after the fat load. Ingestion of both carbohydrate and fat induced substantial rises in GIP secretion, but the protein meal had no effect. In a second study, eight subjects consumed 75 g glucose or the equivalent portion of complex carbohydrate as boiled brown rice or barley. Plasma GIP, insulin and glucose levels increased after all three meals, the largest increase being observed following glucose and the smallest following the barley meal. Plasma GLP-1(7-36)amide levels rose only following the glucose meal. In the 24-h study, plasma GLP-1(7-36)amide and GIP concentrations were increased following every meal and remained elevated throughout the day, only falling to fasting levels at night. The increases in circulating GLP-1(7-36)amide and GIP levels following carbohydrate or a mixed meal are consistent with their role as incretins. The more sustained rises observed in the daytime during the 24-h study are consistent with an anabolic role in lipid metabolism.

Hypoglycaemia in the adult

Hypoglycaemia is a relatively common cause for referral of patients to the accident and emergency departments of hospitals but most of it is iatrogenic. Occasionally, however, hypoglycaemia is due to any one of up to a hundred different disorders. In some, hypoglycaemia is the cause of intermittent neuroglycopenic symptoms that lead to their referral to medical outpatients for investigation. Only the most important are discussed here. Hyperinsulinism due to abnormal beta-cell function is an uncommon but important cause of spontaneous hypoglycaemia. The diagnosis is suspected from the history of episodes of altered consciousness confirmed by demonstrating raised plasma insulin, C-peptide and proinsulin levels in peripheral blood in the presence of hypoglycaemia. Differentiation of the various causes of endogenous hyperinsulinism before surgery is difficult if not impossible and the low predictive value of most of the localizing techniques that are available makes them an additional and unnecessary cost, producing little clinical benefit. Hypoglycaemia caused by non-islet cell tumours (NICTH) is seemingly rarer than hyperinsulinism from insulinoma and tends to occur in older patients. The clinical features are similar to those of hyperinsulinism but laboratory investigation reveals appropriately depressed plasma insulin, C-peptide and proinsulin levels in the presence of hypoglycaemia. The plasma IGF-II:IGF-I ratio is characteristically high and the concentration of the E-domain of proIGF-II is raised. Autoimmune hypoglycaemia is more common in some countries than others and is most often due to autoantibodies to insulin (AIS). It may also be caused by autoantibodies to the insulin receptor and possibly to autoantibodies that are stimulatory to pancreatic beta-cells. Contrary to popular belief, idiopathic reactive hypoglycaemia is rare and only one of the possible causes of the postprandial syndrome. It is characterized by a low blood glucose concentration in blood collected during a spontaneous symptomatic episode but not at other times. Its cause is unknown. Other causes of hypoglycaemia include endocrinopathies of various kinds; sepsis including malaria; congestive cardiac failure; hepatic and renal insufficiencies; diverse inborn errors of metabolism; and exogenous toxins, of which alcohol is probably the commonest.

Assessment of the suitability of commercially available SpA affinity solid phases for the purification of murine monoclonal antibodies at process scale

Eight commercially available staphylococcal protein A (SpA) affinity chromatography solid phases were evaluated in order to establish their potential for the large-scale purification of a murine monoclonal antibody (MAb, mIgG1). The antibody was produced in-house, serum-free, in a hollow fibre bioreactor. Solid phases were tested for the effects of salt concentration, pH, and the presence of MAb on ligand leakage and flow rate. These effects were compared using the solid phases in stirred-tank (roller-mixing) and flow-through (packed-bed) modes of operation. Ligand leakage in the absence of MAb was generally at its lowest when the solid phases were used in a flow-through mode. In this mode of operation increasing the inorganic salt concentration and pH of the washing/adsorption buffer from 150 mM at pH 8.6, to 3 M at pH 8.9, typically produced a 10% increase in MAb capacity of the solid phases (20% for Sepharose CL-4B). However, contamination of the purified antibodies was also greatly increased due to an elevated level of background ligand leakage from the matrices. Residual contaminating levels of SpA in affinity purified MAbs were lowest with a low salt (NaCl, 150 mM) glycine (1 M) adsorption/washing buffer. Maximal antibody capacity was achieved for all matrices on frontal analysis (breakthrough curves), as opposed to a pulse mode of use. The largest capacity was found for Prosep A 'high capacity' (12-15 mg/ml column volume), where capacity approached its experimentally determined theoretical capacity (C/Co = 0.5) regardless of its mode of use. The relatively high MAb capacity of Prosep A 'high capacity' was further reflected in a superior dynamic isotherm. Frontal analysis, however, generally resulted in a greater SpA contamination of the purified MAbs. Under these conditions the lowest levels of SpA contamination were found for the Prosep A 'high capacity', and Repligen solid phases (12 ppm) on purifying 12.8 and 4.3 mg of MAb respectively. For the large scale downstream processing of a MAb for therapeutic applications, Prosep A 'high capacity', would appear to be the most appropriate of the solid phases tested.

An investigation of the allergenic constituents of Cladonia stellaris (Opiz) Pous & Vezda ('silver moss', 'reindeer moss' or 'reindeer lichen')

The sensitizing potency of Cladonia stellaris ('reindeer lichen', 'silver moss') extracts was determined in guinea pigs by a modified FCA (Freund's complete adjuvant) test. The lichen showed a moderate sensitizing potency. Similar investigations with pure common lichen constituents revealed a moderate sensitizing potency for fumarprotocetraric acid and atranorin and a weak one for evernic acid, stictic acid and both forms of usnic acid. Although generally weak, (-)-usnic acid was at least 2 x stronger than (+)-usnic acid. After separation of the Cladonia ether extract into 'usnic-acid-free' and 'usnic-acid-containing' fractions, perlatolic acid was identified as the main allergenic constituent of the 'usnic-acid-free' fraction. Stictic, evernic, fumarprotocetraric acid and atranorin were not detectable. Lichens and lichen products generally possess a weak to moderate sensitizing capacity. Compared with common sensitizers of occupational and environmental importance, these products play only a minor rôle.

Alleviation of non-islet cell tumour hypoglycaemia by growth hormone therapy is associated with changes in IGF binding protein-3

The hypoglycaemia caused by non-islet cell tumours is often associated with an increase in plasma insulin-like activity. In many cases there is a relative if not always absolute increase in plasma insulin-like growth factor II (IGF-II). Growth hormone (GH) secretion is almost invariably depressed as is the plasma insulin response to oral glucose. Despite the high concentration of IGFs (i.e. IGF-I and IGF-II) normally found in the plasma of healthy people their potential hypoglycaemic effect is not manifest due to the tightness with which they are bound to specific binding proteins (IGFBPs). Plasma levels of the major binding protein (IGFBP-3), which is GH-dependent, were depressed in three patients with tumour induced hypoglycaemia. Treatment with biosynthetic GH restored IGFBP-3 to levels which were approximately equimolar to total plasma IGF concentrations, alleviated the hypoglycaemia and restored the plasma insulin responses to oral glucose. We suggest that after GH treatment IGF-II is sequestered by stimulated IGFBP-3 in association with a pre-existing acid-labile subunit to form high molecular weight complexes which prevent IGF-II gaining access to tissues receptors through which it exerts its hypoglycaemic effects.

A sensitive enzyme-linked immunosorbent assay (ELISA) for the detection of staphylococcal protein A (SpA) present as a trace contaminant of murine immunoglobulins purified on immobilized protein A

A specific non-competitive enzyme-linked immunosorbent assay (ELISA) has been developed for detecting and quantifying protein A (SpA), present as a trace contaminant of therapeutic murine monoclonal antibodies (McAb) purified on immobilized SpA preparations. The assay employs a microtitration plate system, in which affinity-selected chicken anti-SpA antibodies from the egg yolks of immunized hens provide a specific capture antibody, followed by the addition of standards or sample with a McAb concentration of 1 mg/ml, in conditions unfavourable for Fc binding, and finally an affinity-selected rabbit anti-SpA peroxidase label. The working range of this assay is between 0.5 and 10.0 ng/ml (CV less than 5%), with a lower limit of detection of 0.2 ng/ml (CV less than 10%). This assay was used to evaluate SpA leakage when purifying a serum-free murine IgG1 cell culture supernatant using SpA immobilized on agarose (Protein A-Sepharose CL-4B) or controlled pore glass (Prosep A, high capacity). These gave average antibody SpA contamination levels of 6.7 +/- 1.6 and 2.4 +/- 0.5 (mean +/- SD) parts per million respectively.